apollonin/numphp

<?php

namespace numphp\Slicing;

use numphp\np_array;

abstract class Slice
{
    public static function isValidFormat($str)
    {
        $matches = [];

        static::matchPattern($str, $matches);

        return !empty($matches) && (bool) $matches[0];
    }

    public static function slice(np_array $data, $str)
    {
        list($start, $stop, $step) = static::getOffsets($data, $str);

        $result = [];

        for ($i=$start; $i < $stop; $i += $step)
        {
            $result[] = $data[$i];
        }

        return new np_array($result);
    }

    public static function getOffsets(np_array $data, $str)
    {
        $matches = [];

        static::matchPattern($str, $matches);

        list($start, $stop, $step) = [(int) $matches[1], (int) $matches[2], (int) $matches[3]];

        if (!$start)
            $start = 0;
        elseif($start < 0)
            $start = count($data) + $start;

        if (!$stop)
            $stop = count($data);
        elseif ($stop <= 0)
            $stop = count($data) + $stop;

        $step = $step ? : 1;

        return [$start, $stop, $step];
    }

    private static function matchPattern($str, &$matches)
    {
        preg_match('|^(-?\d*):(-?\d*):?(-?\d*)|', $str, $matches);
    }
}